Hydraulic fracturing of a stratum in mining shale gas/oil is a method that has been performed since a long time ago. For fracturing fluid used in hydraulic fracturing, guar gum is often used as a thicker. In this method, it is necessary to remove fluid pressure-injected into a fracture, after sending a proppant. A removing method can be performed by sending a breaking agent to dissolve guar gum.
Moreover, for fracturing fluid used in hydraulic fracturing, an inorganic material called as a proppant is necessary such that an expanded gap of shale is not closed. A material called as a breaking agent to decompose a water-absorbable resin pressure-injected into a fracture is also necessary.
Patent Documents 1 to 4 (International Publication No. 2012/050187, Japanese Laid-Open Publication No. 2014-134090, Japanese Laid-Open Publication No. 2014-132091, and International Publication No. 2014/092146, respectively) disclose that a water-absorbable resin is used for excavation. On the other hand, Patent Document 5 (Japanese Patent No. 5143073) discloses a use of a water-absorbable resin for paper diaper, and discloses that scavenging iron ion by a chelating agent suppresses decomposition of a water-absorbable resin.
Patent Document 6 (International Publication No. 2013/112664) discloses a method of liquefying a polymer material.
Further, Patent Documents 7 and 8 (Japanese Laid-Open Publication No. 2006-055833 and United States Patent Application Publication No. 2007/0066167) disclose methods of liquefying a water-absorbable resin.
In addition, it has been known that water-absorbable resins are shrunk by a metal salt, in particular, a multivalent metal ion.
Patent Document 9 (United States Patent Application Publication No. 2010/0193244) discloses an excavating fluid additive for reducing and controlling lost circulation in excavation and a method for the same.
Patent Document 10 (United States Patent Application Publication No. 2008/0045421) discloses a cementitious composite composition including a resin-coated proppant.
Patent Document 11 (United States Patent Application Publication No. 2012/0190593) discloses a formulation for fluid loss control and a method for controlling fluid loss in a well.